Blends of polyethylene polymer and paraffin



Jan. 18, 1966 ROEDEL 3,230,191

BLENDS OF POLYETHYLENE POLYMER AND PARAFFIN Filed May 25, 1959 A. VAPORPHASE ETIIYLENE POLYMER B. LIQUID PHASE ETHYLEIIE PLYIIEEIIRMELILBIELITY (IPV) I IIOISTURE PERIIEABILITY ACTUAL 11 MOISTUREPERMEABILITY CALCULATE A. IDO% 90 80 T 60 50 40 30 I0 0% B. 0% I0 20 T0I00% PERCENTAGE COMPOSITION INVENTOR MILTON J. ROEDEL ATTORNEY-desirably high for many purposes. be due, at least in part, to thebranched chain structure United States Patent 3,230,191 BLENDS 0FPOLYETHYLENE POLYMER AND PARAFFIN Milton John Roedel, Wilmington, DeL,assignor to E. I.

du Pont de Nemours and Company, Wilmington, Del.,

a corporation of Delaware Filed May 25, 1959, Ser. No. 815,733 3 Claims.(Cl. 260-485) This application is a continuation-impart of applicationSJN. 504,511, filed April 28, 1955; which in turn is acontinuation-in-part of application S.N. 382,056, filed September 14,1953 (issued as USP. 2,762,791, September 11, 1956); which in turn is acontinuation-in-part of application S.N. 248,445, filed September 26,1951, now abandoned; which in turn is a continuation-in-part ofapplication SN. 98,197, filed June 10, 1949, also abandoned.

This invention relates to a process of polymerizing ethylene to highdensity polymers and more particularly to the polymerization of ethylenein an improved reaction environment and to products produced therefrom.

It is known that ethylene can be ployrnerized under various conditionswith the aid of such catalysts as oxygen, persulfates, dialkylperoxides, azo compounds, and the like. All of these prior processesemploy highly compressed gaseous ethylene, alone or in admixture withorganic or inorganic liquids, and temperatures of 40 C. and above. Suchconditions are commercially feasible, but because of the high pressuresemployed require costly equipment. Also, the polymer obtained underthese conditions, while more resistant to moisture than most otherpolymers, still has a moisture permeability which is un- This isbelieved to and possibly to the high amorphous content.

An object of the present invention, accordingly, is to provide a processfor polymerizing ethylene which avoids the need for using costly, highpressure equipment and which produces ethylene polymers possessing ahigh degree of linearity, high density, high degree of crystallinity,and which forms films possessing a high degree of -mois tureimpermeability. Another object is to provide ethylene polymer blends.Other objects and advantages of the invention will hereinafter appear.

The above and other objects of the invention are realized by coolingethylene below its critical temperature of 9.6 C. under sufiicientpressure .to liquefy the ethylene, and then polymerizing the ethylene toa solid polymer in liquid ethylene as a reaction medium. For mosteflective operation of the process, the polymerization is carried out inthe presence of an ethylene polymerization catalyst and under variousother conditions hereinafter specified.

Useful catalysts for the process include the metal alkyls, the aliphaticazo compounds of Hunt US. 2,471,959, issued May 31, 1949, peroxygencompounds, and other compounds which yield reactive free radicals below9.6 C. The activity of the metal alkyls is im proved by certain metals,viz., copper, silver, gold, iron, cobalt, and nickel, or their salts.The activity of the peroxygen compounds is improved by silver ions orions of one or more polyvalent metals of atomic number 22 to 29,inclusive (titanium, vanadium, chromium, manganese, iron, cobalt,nickel, and copper) in their lower state of oxidation, ferrous ionsbeing preferred for economic and other reasons. The polyvalent metal ionmay either be introduced in the lower state of oxidation or reduced insitu by a supplementary reducing agent, such as bisulfites,thiosulfates, sulfinic acids, benzoin, l-ascorbic acid, primary,secondary, and tertiary amines, sodium formaldehyde, sulfoxylate, andlike reducing compounds.

The following examples illustrate in detail how to produce polymers ofethylene possessing a high degree of moisture impermeability.

EXAMPLE I A 325 cc. stainless steel shaker tube was charged with 100 cc.of methanol and 1.0 gram of l-hydroxycyclohexyl-l-hydroperoxide,commonly known as cyclohexanone peroxide. The tube was then flushed withnitrogen, evacuated to constant pressure to remove the nitrogen andcooled to about 50 C. in a dry ice/methanol bath. There was then addedto the cold tube 2.0 cc. of 0.090% solution of ferrous chloridetetrahydrate in methanol which is a ferrous ion concentration based on100 grams of monomer of 5 parts per million. There was also added 1.0gram of i-ascorbic acid plus 12 cc. of methanol. The tube was flushedwith nitrogen, evacuated, cooled to about 50 C. and charged with 108grams of liquid ethylene. The tube was then placed in a shaker machineand the machine started. After the tube had warmed up to 20 C. it wasremoved from the shaker machine and totally immersed in an ice/ice watermixture and thus maintained at 0 C. for 18 hours. The pressure droppedduring this period from 1410 lb./sq. in. to 1010 lb./sq. in. Theunreacted ethylene was bled off at 0 C. and the tube opened. Adispersion of ethylene polymer in methanol had formed. The ethylenepolymer was filtered oil and washed first with methanol, then water andfinally with acetone. The yield of solid ethylene polymer was 14.1grams. A hot pressed film of the polymer was hard and stiff. The meltingpoint was 120 C. The moisture permeability value was less than 10 unitsand the density was 0.9745 g./cc. at 25 C.

EXAMPLE II A 325 cc. stainless steel shaker tube was charged with 1.0cc. of 0.90% methanol solution of ferrous chloride tetrahydrate, themethanol evaporated off with an air stream, and then 1.0 gram ofl-ascorbic acid and 1.0 gram of l-hydroxy-cyclohexyl-l-hydroperoxidewere added. The tube was flushed with nitrogen, evacuated, cooled toabout -50 C., and 173 grams of liquid ethylene was added. The tube waswarmed to 3 C. in a shaker machine and the pressure released to 4500lb-./ sq. in. whenever it exceeded 4500 lb./sq. in. The tube was thenimmersed in an ice/ice water bath and maintained at 0 C. for 19.5 hours.The pressure dropped from 4500 lb./sq. in. to 4100 lb./sq. in. duringthis period. The unreacted ethylene was then bled off at 0 C. and thetube opened. The solid polymer of ethylene was obtained as 2. Hull whichafter washing with water, methanol, and acetone, possessed a meltingpoint of 118 C. and gave a very stiff film.

EXAMPLE III A 325 cc. stainless steel shaker tube was charged with cc.of tertiary butyl alcohol, 10 cc. methanol, 1.0 gram l-ascorb'ic acidand 1.0 gram of l-hydroxy-cyclohexyl-l-hydroperoxide. The tube wasflushed with nitrogen, evacuated, cooled to about 50 C. and 5.0 cc. ofan 0.18% solution of ferrous chloride tet-rahydrate in methanol wasadded. The tube was again flushed with nitrogen, evacuated, cooled toabout -50 C. and grams of liquid ethylene was added. The tube was cooledto 80 C. in a shaker box and immersed in an ice/ice water bath at 0 C.for 17.5 hours. During this time the pressure ranged from 530 to 550'lb./ sq. in. The unreacted ethylene was bled oil at 0 C. A dispersionof ethylene polymer in alcohol was obtained. The ethylene polymer waswashed with water, methanol, and acetone. The yield was 7.2 grams ofsolid, powdery ethylene polymer. The melting point was 126.5 C. A hotmolded article was hard, stiff, glossy, mar-resistant and possessed aden- EXAMPLE IV A 325 cc. stainless steel shaker tube was charged with100 cc. methanol and 1.0 cc. of tertiary butyl perbenzoate. The tube wasflushed with nitrogen, evacuated and cooled to about 50 C. There wasthen added 2.0 cc. of a 0.090% solution of ferrous chloride tetrahydratein methanol, 1.0 gram l-ascorbic acid, and 12 cc. methanol. The tube wasagain flushed with nitrogen, evacuated and cooled to about 50 C., and100 grams of liquid ethylene was added. The tube was agitated in ashaker box, while the contents warmed to C. The tube was immersed in anice/ice water bath and maintained at 0 C. for 17 hours. The pressureranged from 560 to 870 lb./sq. in. Unre acted ethylene was bled off at 0C. and the tube opened. A dispersion of ethylene polymer in methanol wasobtained. The dispersion was filtered, the ethylene polymer was washedand dried. The solid ethylene polymer thus obtained had a density of0.9737 g./cc. at 25 C. and moldings were hard and stitf.

EXAMPLE A four-liter stirred, stainless steel autoclave was charged with850 grams tertiary butyl alcohol, 75 grams methanol, grams succinic acidperoxide, and 10 grams of l-ascorbic acid. The autoclave Was thenevacuated, cooled to 0 C. and 100 grams of liquid ethylene was addedwith cooling to 0 C. Thereafter there was added at 0 C. 75 grams ofmethanol and 2.0 cc. of a 0.90% solution of ferrous chloridetetrahydrate in methanol. Polymerization was carried out for 4 hours at12 C. at a pressure of 55 0- 560 lbs./ sq. in. Unreacted ethylene wasbled off and the autoclave discharged at 0 C. A dispersion of ethylenepolymer was obtained. The polymer was filtered off and washed well withmethanol. The solid ethylene polymer obtained was stiff in the form ofbars and films and melted at 123 C.

EXAMPLE VI for 2% hours at 0 C.2 C. at an autogenous pressure of 570-600lbs/sq. in. Unreacted ethylene was bled off at 0 C. and the autoclavedischarged at 0 C. A dispersion of ethylene polymer was obtained. Thedispersion was coagulated by addition of an equal volume of water,

.filtered, the ethylene polymer was washed first with water and thenwith methanol. The solid ethylene polymer was stifi in the form of barsand films and possessed a density of 0.9709 g./cc. at C.

EXAMPLE VII A 325 cc. stainless steel lined shaker tube was charged with90 cc. methanol and 1.0 gram of sodium formaldehyde-sulfoxylatedihydrate. The tube was then flushed with nitrogen, evacuated, andcooled to about 50 C. There were then added 1.0 cc. of a 0.090% solutionof ferrous chloride tetrahydrate in methanol, 9 cc. methanol,

and 2.0 grams 1-hydroxycyclohexyl-l-hydroperoxide. The tube was againflushed with nitrogen, evacuated and cooled to about 50 C., 100 grams ofliquid ethylene was added, the tube warmed to 0 C. in a shaker machine,and

immersed in an ice/ice water bath at 0 C. for 18 hours.

The pressure ranged from 620650 lbs/sq. in. during this period. Theethylene polymer dispersion formed was filtered, and the ethylenepolymer washed first with methanol, then with Water, and finally withmethanol. The solid polymer obtained was stiff in the form of bars andfilms and possessed a density of 0.9858 g./cc. at 25 C.

EXAMPLE VIII A solution of 4 grams of benzoyl peroxide and 0.15 gram offerric acetylacetonate in ml. of thiophenefree benzene was charged intoa 1600 ml. stainless steel autoclave. A test tube containing 4 grams oftriethanolamine was suspended in the autoclave so that its contentswould be emptied when the autoclave was rocked. The autoclave wasflushed three times with nitrogen, cooled in Dry Ice, evacuated andcharged with 280 grams of liquid ethylene. The autoclave was thenbrought to a temperature of 0 C. and rocked for 20 hours. The reactionmixture was discharged and the ethylene polymer removed by filtration.The melting point of the polymer was C.

EXAMPLE 1X A solution of 4 grams of benzoyl peroxide in ml. ofthiophene-free benzene was charged into a 1600 ml. stainless steelautoclave. A solution of 2.5 grams of benzene-sulfinic acid in 40 ml. ofmethanol was added, and 0.1 gram of ferrous chloride in 10 ml. ofmethanol in a test tube was suspended in the autoclave so that thecontents of the test tube would be discharged on rocking. Two hundredgrams of liquid ethylene was charged into the autoclave in the mannerdescribed above, and the autoclave rocked for 20 hours at 0 C. Theproduct was a white powder having a density of 1.096 g./ cc. at 25 C.

EXAMPLE X A mixture of 50 cc. of thiophene-free benzene and 330 cc. ofmethanol was charged into a 1600 cc. stainless steel autoclave and asolution of 2 grams of ammonium persulfate in 5 cc. of Water and 5 cc.of methanol was added. A test tube containing 2 grams of sodiumbisulfite, 0.002 gram of ferrous ammonium sulfate, 5 cc. of water and 5cc. of methanol was suspended in such a manner that rocking theautoclave would discharge the contents of the tube. Two hundred grams ofoxygen-free liquid ethylene was charged in the manner described aboveand the autoclave rocked at 0 C. for 20 hours and ethylene polymer wasisolated as a white powder.

EXAMPLE XI A solution of 5 cc. of dibutyl zinc in 75 cc. of benzene and25 cc. of methanol was charged into a 1600 cc. stainles steel autoclavewhich had previously been flushed with nitrogen. A test tube containing4 grams of powdered, hydrated cupric sulfate was suspended in theautoclave in such a manner that rocking would discharge its contents.The autoclave was charged with 200 grams of liquid ethylene in themanner described above and then rocked at 0 C. for 20 hours. Unreactedethylene was bled off and steam was blown through the reaction mixtureuntil the benzene and methanol had been removed. A small amount ofnitric acid was then added to dissolve the zinc and copper salts. Thewhite solid which remained was washed with water, methanol and acetone,then air-dried to give a flufiy white powder. This polymer had a densityof 0.965 g./ cc. at 25 C. The bending modulus of hot pressed films was113,000 lbs/sq. in.

EXAMPLE XII A 325 cc. stainless steel tube was charged with 95 cc.methanol plus 1.0 gram sodium formaldehyde sulfoxylate and 2.0 cc. of0.09% ferrous chloride tetrahydrate in methanol solution. The tube wasflushed with nitrogen, evacuated, cooled to about -50 C. and 2 cc. oftertiary butyl hydroperoxide in 5 cc. of methanol added. The

tube was again flushed with nitrogen, evacuated, cooled to about -50 C.and 100 grams of ethylene condensed within the tube. The tube andcontents were agitated in a shaker box while the contents warmed up to 0C. and were then immersed in ice/ ice water and maintained at 0 C. for18.5 hours. The pressure during this period was 620-660 lb./ sq. in.Unreacted ethylene was bled off at 0 C. and the tube opened. Theethylene polymer dispersion was filtered off, washed well with methanoland dried. The density of this ethylene polymer was 0.9944 g./cc. at 25C.

EXAMPLE XIII To a 400 cc. stainless steel vessel was added 40 cc.methanol, cc. of water, and after cooling to C., 1 gram of potassiumazodisulfonate. The vessel was sealed, evacuated, and cooled to 80 C.and 150 grams of liquid ethylene was bled in. The vessel was immersed inwater at 0 C. for 24 hours, with the contents agitated by slowlyrotating the vessel end over end. Unreacted ethylene was discharged andthe tube was opened. A solid material amounting to 1.2 grams wascollected. This product was waxy, insoluble in acetone or cold xylenebut soluble in hot xylene.

EXAMPLE XIV A 400 cc. silver-lined vessel to which had been added 0.5gram nickel-on kieselguhr catalyst was dried by heating several hours at100 C. under a pressure of 0.5 mm. mercury. The vessel was evacuated and150 cc. benzene containing 5 grams of lithium butyl was added underanhydrous conditions. The vessel was pressured with 150 grams ofethylene. The vessel and contents were rotated slowly end over end for9.5 hours at 0 C. Unreacted ethylene was bled off. The solid polymerwhich formed was washed with water, dried and dissolved in hot xylene.The latter solution was added with stirring to an excess of methanol andthe ethylene polymer was recovered and dried. The solid polymer meltedat 128.4" C., as determined by observing the disappearance of speruliteson a hot stage microscope.

EXAMPLE XV To a glass-lined vessel was added 2 grams ofN-nitrosoacetanilide (prepared according to Johnson and coworkers, I.Am. Chem. Soc. 65, 2446 (1943)) and 2 grams of dry thiophene-freebenzene. The vessel was evacuated, cooled in liquid nitrogen andethylene distilled in until the vessel was about one-third full ofliquid ethylene (about 120 cc.). The reaction mixture was maintained at0 C. for 11 days. The vessel was opened and unreacted ethylene allowedto escape. The solid material which was adhering to the walls of thereaction vessel was washed w th acetone and dried. Five grams of Waxysolid was collected which melted at 119 C. (hot stage microscope). Itwas insoluble in cold xylene but dissolved on heating in this solvent.

The polymerization of ethylene can be carried out in liquid ethylene asthe sole reaction medium or in the presence of an organic medium whichremains liquid below the critical temperature of ethylene (9.6 C.).Typical of such liquids are methanol, tertiary butanol, isooctane,toluene, xylene, and combinations thereof. Mixtures of water and organicliquids which are water soluble can also be used, if desired. Preferredreaction media are methanol, tertiary butanol, and benzene.

Emulsifying agents can be included in the reaction mixture, if desired,and examples are the potassium and sodiurn salts of long chain aliphaticcarboxylic acids, the sodium and potassium salts of long chain alcoholsulfates or sulfonates, neutral agents such as the polyethylene oxidecondensates, and quaternary ammonium salts, as well as other emulsifyingagents common to the art.

The pH of the reaction medium may be varied within wide limits,depending upon the system used.

The temperature of the polymerization may be varied, from the criticaltemperature, which is 9.6 C. for ethylene, to temperatures of 50 C. orlower, the essential feature being when operating in this lowtemperature range that the ethylene be present as a liquid phase so thatonly nominal pressures are required to achieve a satisfactory monomerdensity that will lead toa high molecular weight, solid polymer ofethylene on polymerization. The pressures to be employed depend upon thenature of the polymerization medium and the degree of polymerizationdesired but must be sufiicient to insure that the ethylene be present asa liquid phase with none, or at most an inconsequential part, present asa vapor phase. Pressures in the range of 10 to atmospheres are normallysufiicient. Higher pressures, e.g., up to 2000 atmospheres may, however,be used.

The examples illustrate a number of methods in which highly effectivecatalysts for the polymerization of ethylene are used. Some of thesemethods involve a system in which a peroxygen compound is dissociated inthe presence of a polyvalent heavy ion in a lower valence state. Theheavy metal ion is oxidized to its higher valence state and theperoxygen compound is reduced. The presence of the heavy metal is notcritical for operativeness but its use in combination with peroxygencompounds constitutes a preferred mode of operation.

A preferred method of producing a reduction-oxidation catalyst forconducting polymerizations in accord with the invention has beendescribed, generally there being used in such a method a polyvalentheavy metal, an oxidizing agent, and for optimum results, a reducingagent to maintain the metal ion in the reduced state.

Examples of suitable oxidizing agents which also function as freeradical producers include the peroxygen compounds, e.g., the salts ofhydrogen peroxide, perborates, percarbonates, persulfates,perphosphates, percarboxylates; organic hydroperoxides such as methylhydroperoxide, ethyl hydroperoxide, tertiary butyl hydroperoxide,tetralin hydroperoxide, cumene hydroperoxide, 1-hy' droxycyclohexylhydroperoxide-l, and numerous hydroperoxides obtained by adding one moleof hydrogen peroxide to a carbonyl group to obtain the groupingdiacylperoxides such as benzoyl peroxide, acetyl peroxide, acetylbenzoyl peroxide, lauroyl peroxide, tricholroacetyl peroxide, crotonylperoxide, etc.; alkyl acyl peroxides such as tertiary butyl perbenzoate,ditertiary butyl perphthalate, tertiary butyl permaleic acid, tertiarybutyl perphthalic acid; hydrogen peroxide, peracetic acid, perbenzoicacid, di-isobutylene ozonide, methyl ethyl ketone peroxide,acetone-methyl isobutyl ketone peroxide, succinic acid peroxide, methylisobutyl ketone peroxide, dibenzal diperoxide, polyeroxides, diethylperoxydicarbonate, isopropyl percarbonate, pelargonyl peroxide and likematerials. Amounts used are in the range of 0.005 to 3% by weight basedon monomer.

The amount of heavy metal as a salt added to the polymerization mixturecan be markedly lowered by the addition of an organic reducing agentwhich possesses the ability to reduce the valence of the metal, thusrenewing the supply of unreduced metal when the reduced metal isoxidized. Under these conditions the amount of ferrous salt present, forexample, is preferably in the range of 1-1000 parts per million based onthe total amount of polymerizable monomer present. The rate ofpolymerization is markedly influenced by the amount of ferrous metalpresent with 100 parts per million giving much faster rates than 10parts per million. The heavy metal can also be obtained by introductionof a simple or complex salt or compound in which the metal is present inthe oxidized state provided that a suitable reducing agent is present toreduce it. Examples of such reducing agents are manifold and includesuch compounds as l-ascorbic acid, d-ascorbic acid, sodium formaldehydesulfoxylate, dihydroxymaleic acid, formamidine sulfinic acid, butyr- 8In the drawing, graphically shown by curve I, is represented themoisture permeability of a blend of liquid phase ethylene polymer andvapor phase ethylene polymer plotted against percent composition. Theordinate is dialdehyde, sorbose, levulose, inosose, fructose andglucose. vided in moisture permability units, the values given repre-These reducing agents are generally used in amounts of senting the gramsof water transmitted per hour at a 0.005 to 3% based on the total amountof monomer temperature of 39.6 C. per 100 sq. meters of surface areapresent. for film l-mil thick with 100% relative humidity on oneAliphatic azo compounds operable in the practice of this side of thefilm and zero percent relative humidity on the invention are those whichhave an acyclic azo, N=N, 10 other side. The abscissa is divided inpercentage comgroup and which decompose to yield free radicals beloposition by weight of the blended mixture. The blends 9.6 C. Examplesare alpha, alpha-azo-diisobutyric acid, were made from an ethylenepolymer having a density alp P P gamma-dimethyl-gamma' of 0.9137 g./ cc.at 25 C. prepared from gaseous ethylene methOXYVaIeTOIIitYiIe), p P P atelevated temperatures and superatmospheric pressures gamma-dimethy-gammaethoxy valefollitfile), p and a liquid phase ethylene polymer producedin accord p p gamma, gamma trimethylvalel'o' with the process of theinstant case, having a density of nitrile), alpha, alpha-azobis(alpha,gamma-dimethyl- Q9757 at 25 c gamma-butoxyvalefonitfile), alpha, P P Thestraight line of the drawing II represents the moisgamma-dimethyl-gamma-phenylWalerenitrilel, alpha, ture permeabilityvalue that would be obtained if the P p 'p y p p Potasslnm aZOdl'properties of the blended polymers were additive using Sulfonate, andthe like. These compounds may be the moisture permeability value of theliquid phase pared by the procedue described in US. Patent 2,469,358,polymer as Substantially Zeta issued y 10, 1949 to Aldel'son and RobertFrom curve I it will be noted, inter alia, that the addi- 8011- tion of20% of the ethylene polymer obtained by polyme t y e P y Produced by theProcess erizing liquid ethylene below its critical temperature to ofthis invention with densities of at least 0.94, are 80% of ethylenepolymer obtained by polymerizing gase markedly dlflerent 1n Physlcel1Propernes from ethylene ous ethylene at elevated temperatures andpressures, re- PPlyIneTs Obtained by polymerizing ethy1ene under ducedby 50% the moisture permeability of the latter nlgn Pressures: 1500atmospheres wlth densltles polymer whereas if the blend properties wereadditive the tweenabout 0.91 an d 0.925. The homopolymer of the moisturepermeability could only have been reduced by lnventlon have a,mm1m,um ofChat branches less 20%. This constitutes persuasive evidence that thesetwo than one atkyl Stde chatn Per 200 carbon tittoms m the polymers mustnecessarily possess entirely different struc- Polymer motectfle n m tcan be Consldered to be tures although they are both prepared fromethylene. more g 1655 ,hnear m then molecular Structure t A further andoutstanding diiference between the liquid shcfrt slde t .When presente6speclauy In low itensttlfl phase polymers and the vapor phase polymersof ethylene Po g t Contam m the Order of atoms more or 0 is demonstratedby the difference in their Youngs bending f on m t and more than 7 atoms0t carbop modulus. Films of the polymer from gaseous ethylene eseparatmg the branches The f exhibited a modulus from 14,000 to 24,000p.s.i. com described m P s Branchmg m Poty' pared to a modulus of100,000 to 200,000 p.s.i. for films ethylene Durmg Polymerization, M. J.Roedel, 75, 6 110 40 (1953) This substantially linear structure of thehigh of the polymer from hqmd ethylena density polymers is chemicallydifferent from the molecu- The difference between-these polymers ishkewl-se shown 7 1 t f th 10W densit 01 mars which have by the fact thatthedensrty values are not add1t1ve for a at Struc o e y p y 70/30mixture of ethylene polymer made by polymerizing more than one atkytstde Chant Per 100 Carbon atoms m liquid ethylene below its criticaltemperature with ethylene the P m molecule Moreover the homopolymers oftemperatures and pressures (densities 0.9137/0.9757). the lnventton aresllbstaneany free from oxygen and This mixture possesses a density of0.9335 whereas by adtain no carbonyl groups substantially, as determinedby ditive calculation the dnsity Should be 9323. infra-red analysis. Thedilference between the polymers In Table I a number of blends are Showntogether with of the inventien and the Pnlymers of the art 15 one oftheir bending modulus, density, water vapor permeability kind ratherthan 0116 of degree as is demonstrated by e together with the change ofdensity imparted to the lower fact that the moisture permeability valuesare not add1- density polymfir of h blend and h incremental i tive whenthe pOlYlTlfil'S are blended together. Attention provement in itsmoisture vapor permeability, One of is directed to the drawing whichillustrates the difference th t t di values f th bl d li i th i i inkind which exists between the polymers of ethylene proved stiifness andRV. and their enhanced potential to known to the art and the polymers ofethylene prepared provide a series of packaging materials with improvedaccording to this invention. combinations of stifiness and RV.

Table I POLYMERS Bending Modulus, Density RV. Dd DPV A B p.s.l. (Amount(Amount by weight) by weight) 0 20 125, 000 0. 9757 can A=Low densitypolyethylene; B =High density polyethylene.

Grams of water vapor transmitted per hour per sq. meters for 1 mil thickfilm at 39.6 C. and 100% relative humidity on one side+0% relativehumidity on the other side The addition of 20% of the high densitypolyethylene to the low density polyethylene doubles the stifiness andhalves the moisture permeability of the latter.

In addition to the blends hereinbefore described and to the linearpolyethylene paraffin wax blend of Example III, blends with otherpetroleum waxes are within the purview of the invention such, forexample, as blends of linear polyethylenes, having densities between .94up to the maximum densities of such polymers, with parafiin wax,candelilla wax, carnauba wax, montan wax, spermaceti wax,microcrystalline wax, and amorphous petroleum wax, separately or incombination, having melting points between 120 F. and 180 F. andpreferably between 145 F. and 165 F. and these waxes preferably havingan oil content of less than 0.5 percent. Moreover, those waxes having ahardness range of 10 to 35, needle point penetration at 77 F.,ASTM-D-S-ZS, are most suitable.

The addition of petroleum wax and especially microcrystalline wax, up toa level of to by weight, to linear polyethylene, results in an increasein melt index (ASTM-D-1238-52T). The addition of up to 5% pctroleum waxto linear polyethylene results in a sharp increase in stifiness, areduction of internal haze, above about 5% wax, little change instifiness is noted. The tensile properties, such as yield strength,ultimate strength, and ultimate elongation, reach a maximum which occurswith the blending of about 1% of the paraffin wax with the linearpolyethylene, such blends also had improved transparency.

it eminently suitable for plastic outlets requiring good rigidity suchas synthetic fibers, monofils, piping, electrical insulation and manykinds of fabricated articles. The outstanding moisture irnpermeabilityof these ethylene polymers makes the polymer obtained by polymerizingliquid ethylene well suited as a protective wrap for foodstutfs,cigarettes, baked goods, and the like.

The high moisture-vapor impermeability and high stiffness of the highdensity polymers of the invention and their equivalents, as hereinbeforedescribed, make these polymers especially useful for the preparation oflaminated products. The high density polymers with less than one alkylside chain per 200 carbon atoms in the molecule as a lamina impart theirsuperior properties to laminates of a wide variety of thermoplasticssuch as the cellulose esters and ethers, e.g., cellulose acetate,cellulose nitrate, ethyl cellulose, cellulose acetobutyrate, etc.; thepolymers such as the acrylate and methacrylate resins, polyamides,polystyrenes, polyvinyl acetates, and more especially, the low densitypolymers of ethylene. Flexible laminated films of one or more laminae ofthe high density homopolymers of ethylene with one or more laminae ofthe low depsity polymers of ethylene are especially useful for wrappingpurposes, for the production of sheets, and uses generally where addedstilfness and improved P.V. are required. The laminates may be made byhot pressing, with or without the use of a mutual adhesive, one laminato Table II Linear Micro Tensile Ultimate Trans- Polycrystalline MeltStiffness Yield parency ethylene wax Index (p.s.i.) (percent) (parts)(parts) Elong. Strength (percent) (percent) A B A=Filmz milthickimmediately after molding. B=Filmz mil thiek1 week after molding.

Any suitable process may be used for preparing the blends such, forexample, as by the Banbury mixers, roll mills, extrusion mixers or bythe solution blending processes well known to the plastic art. Moreover,the resulting blends may be formed into the ultimate product by solutioncasting, extrusion molding, injection molding, pressure molding, and thelike, to form supported or un supported films, rods, or other desiredshapes.

The high density polymers can be made by processes other than thosedescribed in the Examples I through XV. Any suitable process can be usedproviding it produces an ethylene polymer having a density of more thanabout 0.94 and especially if it produces substantially linear polymerswith less than one alkyl side chain per 200 carbon atoms in the polymermolecule, with a melt index ASTM- D1238-42T) of less than 500. (The meltindex of low density polymers is 10 or below.) Other processes forproducing high density polymers are described in the US. Patents ofLarchar and Pease, 2,816,883, issued Dec. 17, 1957; and Pease andRoedel, 2,762,791, issued Sept. 11, 1956.

The very high stiffness and the outstanding moisture impermeability offilms of the polymer obtained by polymerizng liquid ethylene below thecritical temperature make References Cited by the Examiner UNITED STATESPATENTS 2,523,705 9/ 1950 Lovell et al. 260--28.5 2,762,791 9/ 1956Pease et al 260-949 2,816,883 12/1957 Larchar et al. 2,825,721 3/1958Hogan et al. 2,882,246 4/ 1959 Leatherman et a1. 26028.5 2,504,2704/1960 MacLaren et al 260-285 MORRIS LIEBMAN, Primary Examiner. DANIELARNOLD, ALPHONSO D. SULLIVAN, MIL- TON STERMAN, ALEXANDER H. BRODMERKEL,

Examiners.

1. A HOMOGENEOUS BLEND CONTAINING 80 PARTS BY WEIGHT OF PARAFFIN WAX AND20 PARTS BY WEIGHT OF A SOLID LINEAR ETHYLENE POLYMER HAVING A DENSITYMORE THAN ABOUT 0.94.